1. Field of the Invention
The present invention relates to a novel use of a cereal extract as a slimming active agent in a slimming cosmetic composition, and also to a cosmetic care method using said composition.
2. Prior Art
Adipose tissue plays a central role in controlling the energy balance of the organism. It is constituted of aggregate cells, adipocytes, and of an abundant connective-vascular stroma. Adipocytes (or adipose cells) can either store energy in lipid form (essentially triglycerides), or release this energy into the extracellular medium in the form of fatty acids and glycerol. To do this, the adipocyte contains an enormous lipid vacuole, which is approximately 80% of the cell mass.
These lipids are placed in reserve by esterification of fatty acids in the form of triacylglycerols (lipogenesis). The latter can be hydrolyzed by triglyceride lipase, thereby allowing these fatty acids to be released into the blood stream (lipolysis).
Mature adipocytes, located in the hypodermis, are formed from adipocyte precursors, or preadipocytes, which are fibroblast-type cells that can differentiate into adipocytes in the adipose tissue. After a growth phase, the preadipocyte experiences a pause in cell multiplication. It then enters into the process of adipocyte differentiation.
During terminal differentiation, adipocytes exhibit a considerable lipogenic capacity. This results in the gradual accumulation, in the cytoplasm, of lipid vacuoles which will subsequently fuse. This step is up- or down-regulated by factors in the surrounding medium, such as hormones, cytokines, growth factors or vitamins.
The adipocyte differentiation process is also accompanied by changes in the nature of the expression and in the composition of cell surface proteins known as “integrins”.
These integrins each have a large extracellular segment, a transmembrane segment and a cytoplasmic segment which is generally very short and devoid of enzymatic activity.
The integrins can be likened to receptors for molecules that make up the connective tissue. They represent a family of heterodimers located at the surface of cells and each composed of an α-subunit and of a β-subunit which are noncovalently associated: fourteen isoforms are known for the α-chain and nine isoforms are known for the β-chain. These α and β isoforms associate with one another in various ways so as to give rise to more than 20 receptors, which confers great diversity on the system.
The integrins are involved in intercellular adhesion and cell-extracellular matrix protein (laminin, fibronectin, collagen, vitronectin, etc.) adhesion. Inside cells, the cytoplasmic segment of the integrins is associated with varied proteins of the cytoskeleton, such as talin or α-actinin. The transmembrane segment not only promotes the regulation of adhesion, but also makes it possible to transmit intracellular signals which can modify the behavior of the cell (stationary state, migratory state, proliferation, secretion, etc.).
The integrins also have a role in transduction signals and gene regulation. It has been shown that the α5 and α6 integrins, which are respectively receptors for fibronectin and for laminin, act reciprocally to regulate proliferation and differentiation of preadipocytes into adipocytes (Liu J et al., Cell Metab. 2005 September; 2(3):165-77). The authors have shown that the more α5 integrin is expressed, the less the cells enter into differentiation. The α5 subunit is greatly expressed in preadipocytes but is undetectable in adipocytes; conversely, the α6 subunit is undetectable in preadipocytes and abundant in adipocytes.
Cells which overexpress α5 integrin maintain a fibroblast phenotype with few lipid droplets. The overexpression of α6 integrin in cells, 5 days after induction of cell differentiation, induces the synthesis of intracellular triglycerides.
A switch in integrin protein expression thus takes place during the adipocyte differentiation process, between α5 integrins, which keep the cells in an undifferentiated state (preadipocytes) and α6 integrins, which “control” the signaling process leading to terminal differentiation into adipocytes.
FR 2 893 504 (SILAB) discloses an extract of cereals and/or of legumes, said extract being obtained in an aqueous medium. This extract is used as an active agent in cosmetic compositions for obtaining an anti-aging, and in particular antiwrinkle, effect.
FR 2 893 504 does not suggest, for this extract, any effect with respect to integrin expression in the cells of the adipose tissue of the skin, and does not envision, for this extract, any use as a slimming active agent in cosmetic compositions.